When a metal material is subjected to plastic working, such as forging, extrusion, drawing, rolling or pressing, a lubricant film must be disposed on the surface of the metal material and/or the molding surface of the metal mold to reduce friction between the material and the mold and the prevent the generation of drag, seizures and the like.
In most cases, the metal is immersed in a zinc phosphate solution to produce a zinc phosphate or iron phosphate chemical film (hereafter referred to as “phosphate film”) on the surface, and then further immersed in a sodium soap or the like to produce a metallic soap layer on the surface. This process creates a surface protective layer of satisfactory quality, and allows heavy working (meaning working of material surfaces with large elongation rates). However, this process requires washing treatments with cold water, hot water or acid, as well as different types of equipment. Such treatments also require long periods of time, thus lengthening the lead time. Usually, 30 minutes or longer is necessary to complete a series of treatments. It is also necessary to accomplish a single surface treatment of the entire portion of the metal that is subjected to plastic working in a subsequent step during the treatment time, and therefore this process is not suitable for production of small, sundry products.
In order to overcome these problems, the use of working oils has been proposed. For example, Japanese Laid-Open Patent Publication No. 7-118682 teaches a working oil prepared by dispersing in a mineral oil a zinc or molybdenum salt, such as zinc dithiophosphate, molybdenum dithiocarbamate or the like, which has been rendered lipophilic by the introduction of a higher alkyl group. This working oil solves most of the aforementioned problems, but because the main component is oil, it creates problems, such as contamination due to adhesion of the oil to surrounding machines and generation of oil mist. In other words, contamination of the working environment is unavoidable. A number of other problems also remain, such as the need to degrease the material surface after plastic working.